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CU
Study Shows Novel Structure In South Pacific Plant May Be
'Missing Link' In Evolution Of Flowering Plants
May 17, 2006
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Amborella
trichopoda, a
plant species found in rain forests of New Caledonia in the
South Pacific, first appeared on Earth 130-million years ago.
New data provided evidence that this "living fossil"
may be a crucial link between modern flowering plants and
their predecessors.
Credit: Thomas J. Lemieux,
University of Colorado at Boulder
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A new University of
Colorado at Boulder study involving a "living fossil plant"
that has survived on Earth for 130 million years suggests its
novel reproductive structure may be a "missing link"between
flowering plants and their ancestors.
The Amborella
plant, found in the rain forests of New Caledonia in the South
Pacific, has a unique way of forming eggs that may represent a
critical link between the remarkably diverse flowering plants,
known as angiosperms, and their yet-to-be-identified extinct
ancestors, said CU-Boulder Professor William "Ned"
Friedman. Angiosperms are thought to have diverged from
gymnosperms -- the dominant land plants when dinosaurs reigned in
the Cretaceous and Jurassic periods -- roughly 130 million years
ago and have become the dominant plants on Earth today.
"One
of the biggest challenges for evolutionary biologists is
understanding how these flowering plants arose on Earth,"
said Friedman, a professor in CU-Boulder's ecology and
evolutionary biology department, whose study appears in the May
18 issue of Nature. "The study shows that the structure that
houses the egg in Amborella is different from every other
flowering plant known, and may be the potential missing link
between flowering plants and their progenitors."
In
basic terms, Amborella has one extra sterile cell that
accompanies the egg cell in the female part of its reproductive
apparatus known as the embryo sac, according to the study. The
discovery of the unique configuration of the egg apparatus, which
is thought to be a relic of intense evolutionary activity in
early angiosperm history, "is akin to finding a fossil
amphibian with an extra leg," according to a May 18 Nature
perspective piece accompanying Friedman's article.
The
novel embryo sac described in Nature is the first new type of
egg-bearing apparatus to be discovered in flowering plants in
more than 50 years, according to Friedman. "The unique
four-celled egg apparatus in Amborella could represent a critical
link between angiosperms and gymnosperms," he wrote in
Nature.
The origin and evolution of flowering plants has
long confounded scientists, he said. Nearly 130 years ago,
Charles Darwin, known for developing the theory of natural
selection, called the appearance of flowering plants "an
abominable mystery."
The surprising new finding
suggests flowering plants may have arisen on Earth during a time
when plant evolution was "particularly flexible,"
Friedman said.
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By
studying the reproductive structures of the ancient flowering
plant Amborella,
scientists are learning more about evolutionary
processes.
Credit: Thomas J. Lemieux, University of
Colorado at Boulder
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The peculiar egg-forming
structure seen in Amborella may eventually link the odd South
Pacific shrub to gymnosperms such as conifers, said Friedman. "We
associate this structure with a relatively primitive reproductive
process," he said.
Amborella is a small shrub with
tiny greenish-yellow flowers and red fruit that grows only in the
understory of New Caledonia rain forests. Amborella plants are
unisexual, meaning they will produce either all male or all
female flowers. Cross-pollination between plants is required for
fruit production.
Plants used in the study were from both
New Caledonia and from specimens cultivated in a CU-Boulder
greenhouse. Friedman used a combination of laser, fluorescence
and electron microscope techniques during the study.
"My
research and teaching go hand in hand, and this is the kind of
science that goes directly into the classroom," said
Friedman, who oversees the work of six CU-Boulder undergraduates
and graduate students. "The kinds of discoveries we make in
the lab have a profound effect on the material taught in my
courses."
Friedman, who also is a co-investigator at
CU-Boulder's Astrobiology Center, directs several NSF-funded
research efforts. He is the chief scientist for NSF's Molecular
and Organismic Research in Plant History, or MORPH project that
supports training opportunities around the country for students,
postdoctoral fellows and early career professionals. MORPH
focuses on the diversification of plant forms on Earth over the
past 500 million years.
Source
/ Credit: Colorado University
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